Mark 9:28

28 When Jesus went into a house, his disciples asked him privately, "Why couldn't we force the spirit out of the boy?"

Mark 9:28 Meaning and Commentary

Mark 9:28

And when he was come into the house
Perhaps into the man's house whose child he had healed, or into some other in these parts, for the sake both of retirement and refreshment:

his disciples asked him privately, why could not we cast him out?
The nine disciples, who were particularly concerned in this matter, fearing they had lost the power of casting out devils, conferred upon them, inquired of Jesus, when he was alone, why they could not cast the demon out of the child, when they had ejected unclean spirits out of many others; (See Gill on Matthew 17:19).

Mark 9:28 In-Context

26 The evil spirit screamed, shook the child violently, and came out. The boy looked as if he were dead, and everyone said, "He's dead!"

27 Jesus took his hand and helped him to stand up.

28 When Jesus went into a house, his disciples asked him privately, "Why couldn't we force the spirit out of the boy?"

29 He told them, "This kind of spirit can be forced out only by prayer."

30 They left that place and were passing through Galilee. Jesus did not want anyone to know where he was